1. Field of the Invention
The present invention, generally, relates to the servicing of electrical contacts and, more particularly, to a method and apparatus of maintaining electrical contacts clean.
An ideal situation would involve having two sets of electrical contacts for use in a high current application, one set formed of solid silver for use only when there is to be no flow of electrical current during a separation of the contacts and a second set formed of silver cadmium for use when switching is to interrupt a current flow. Such an arrangement has several disadvantages, such as stocking two sets of electrical contacts for each piece of equipment, the resulting confusion when they are mixed up and the excessive cost involved.
2. Description of the Prior Art
Efforts in the past have approached this problem from different viewpoints. One is to provide a mechanical structure that, hopefully, would wipe the contacts to maintain them clean from contamination and another is to provide a structure to eliminate electrical arcing during contact separation in an effort to avoid a major cause of contamination.
U.S. Pat. No. 4,286,311 to Maglica describes a switch arrangement in which one switch contact is rotated each time it is actuated to wipe off dirt and products of oxidation and corrosion between the contacts. Elastomeric seals are constructed between the parts that are separable and movable to seal them hermetically against moisture and dirt.
U.S. Pat. No. 4,616,203 to Kakizoe et al. describes an electromagnetic contactor with particular structurally arranged parts that define an electrical arc-extinguishing chamber to prevent damage and contamination even when the interruption of a large electrical current is carried out repeatedly.
U.S. Pat. No. 4,743,720 to Takeuchi et al. describes the connection of an electromagnetic winding for being energized by the same electrical current that develops an arc between contacts being separated. This electromagnetic winding is located so that the lines of magnetic force that it develops extend transversely of the arc, resulting in extending its length and quickly extinguishing the arc. An electrical circuit includes the electromagnetic winding and a form of magnetic flux diverting yoke.
The prior art describes a number of mechanical structures for maintaining the effectiveness of electrical contacts. One system which occurs most frequently for assuring switch safety provides double contact springs with the contacts arranged in parallel. However, since these contacts are always touching, the cleaning involved, if any, is negligible.
Therefore, the problem persists, and efforts to solve it have concentrated on ways to avoid developing contamination of electrical contacts, such as structures that try to extinguish all arcing between electrical contacts. It has not been until the present invention that a way has been found to use the electrical arc itself to solve the problem of contaminated contacts.